Check if the timeout expired during the time update in qt_safe_select

It can happen that select(2) returns -1 with EINTR, but the time
remaining was too small for us to update the time. Our own processing
(plus the syscall to clock_gettime(2)) leads us past the timeout, so
we get a negative timeval.

Task-number: QTBUG-6755
Reviewed-by: Bradley T. Hughes

1 files changed, 3 insertions, 2 deletions

diff --git a/src/corelib/kernel/qcore_unix.cpp b/src/corelib/kernel/qcore_unix.cpp
index 5885591..d0dc7be 100644
--- a/src/corelib/kernel/qcore_unix.cpp
+++ b/src/corelib/kernel/qcore_unix.cpp
@@ -129,7 +129,7 @@ static inline bool time_update(struct timeval *tv, const struct timeval &start,
     // clock source is monotonic, so we can recalculate how much timeout is left
     struct timeval now = qt_gettime();
     *tv = timeout + start - now;
-    return true;
+    return tv->tv_sec >= 0;
 }
 
 int qt_safe_select(int nfds, fd_set *fdread, fd_set *fdwrite, fd_set *fdexcept,
@@ -154,7 +154,8 @@ int qt_safe_select(int nfds, fd_set *fdread, fd_set *fdwrite, fd_set *fdexcept,
 
         // recalculate the timeout
         if (!time_update(&timeout, start, *orig_timeout)) {
-            // clock reset, fake timeout error
+            // timeout during update
+            // or clock reset, fake timeout error
             return 0;
         }
     }